1. Field of the Invention
The field of the present invention is improvements of intake devices designed to provide an increase in volume efficiency of a multi-cylinder combustion engine by controlling the variation in intake gas pressure in an intake system.
2. Description of the Prior Art
There is an already known intake device for multi-cylinder internal combustion engines, which is designed to increase the volume efficiency in a region of from a lower speed to a higher speed by controlling the length and volume of the intake system in a variable manner in accordance with the operational condition of the engine to accomplish one of two effects: a resonance effect that variations in intake gas pressure resonate between cylinders which produce no suction interference and an inertia effect utilizing the fact that a negative pressure wave produced at the beginning of suction for every cylinder is reflected at an increased volume portion provided in the intake system back to an intake port (for example, see Japanese Patent Application Laid-open No. 169627/85).
The above intake device comprises a pair of resonance chambers defined in the increased volume portion provided in the intake system and communicating with groups of cylinders having such an order of ignition that any one of the cylinders is not ignited immediately before or after ignition of the other cylinders of the same group, and an on-off valve provided between the chambers for permitting the chambers to be put into and out of communication with each other, whereby controlling of the opening and closing of the on-off valve causes the intake system to be switched to a resonance supercharge system or an inertia supercharge system. Further, controlling of the opening and closing of another on-off valve provided between a pair of resonance passages connected to upstream sides of the pair of resonance chambers causes the speed region of the engine permitting accomplishment of a resonance supercharge effect in a lower speed region to be switched at two stages, thereby increasing the volume efficiency over a totally wider speed region of the engine.
When such intake device is disposed in a V-shaped space in a V-shaped multi-cylinder internal combustion engine, it is difficult to suitably dispose the resonance passages and the resonance chambers without hindering the suction efficiency, because the space is extremely narrow. An on-off valve capable of changing the suction characteristics is also provided in a resonance chamber assembly box provided with the resonance passages and the resonance chambers. However, the disposition of the on-off valve within the resonance chamber assembly box causes problems of not only an increase in size of the intake system to create a difficulty in the layout thereof, but also a complication of the structure, resulting in an increased cost of manufacture. Further, in an intake device which is designed to establish a resonance supercharge system or an inertia supercharge system by permitting the resonance passages and the resonance chambers to be put into or out of communication each other through the on-off valve, it is extremely difficult to set the volumes of the resonance passages and the resonance chambers so that both the resonance supercharge effect and the inertia supercharge effect may be optimally accomplished.